Bay Area Fog Disrupts Flights;
United Airlines Is Hit Hard

United Airlines, the largest operator at San Francisco International Airport, was struggling to recover Tuesday after three days of fog threw holiday travel into turmoil in the Bay Area.

The unit of UAL Corp. said it canceled about 20% of its 500 daily San Francisco inbound and outbound flights on Sunday and Monday and an additional 28 flights Tuesday. Bill Roy, United's station manager in San Francisco, said the problem...